Ballroom dancing (USABDA), 7-7:45 p.m., beginner; 8-9 p.m., intermediate; 9 to 11 p.m., open dancing and practice time, Elks Lodge, Cambridge, upstairs ballroom. Cost is $5 for members; $7 for non-members; and $3 for students. Dancers may attend all three sessions for the one price. Dress is casual. For information, call 685-1068 or 432-4130.